Cobalt Nanoparticles Supported on TiO₂ for Highly Selective Formation of <i>N</i>-Benzylideneanilines from Nitroarenes and Benzaldehyde via Reductive Imination Reaction

Abstract

The search for active, inexpensive, and stable heterogeneous catalysts to produce desired imines in fine chemistry presents an ongoing challenge for both academia and industry. This work reports the utilization of Co nanoparticles supported on TiO2 derived from the H2-assisted reduction of the perovskite-type mixed oxide CoTiO3. The entire preparation process is operationally simple and straightforward, enabling scalability for practical applications. The resulting catalyst comprises metallic cobalt nanoparticles responsible for the hydrogenation process, whereas the TiOx thin layer surrounding the cobalt promotes the adsorption of C=O, thereby enhancing the formation of desired products. Notably, at lower temperatures, the reaction yields the target imine product. Our study demonstrates a synergistic effect between nitrobenzene and benzaldehyde in the presence of a Co-TiOx interface, which reduces the apparent activation energy for the hydrogenation of the-NO2 group. Furthermore, under moderate reaction conditions, the catalytic system offers applicability to various nitrobenzene compounds substituted at the 4-position and benzaldehyde, resulting in high yields of the corresponding imines with electron-density-donating substituent groups. Finally, the catalyst exhibits facile separation for subsequent reuse, displaying moderate stability with minimal selectivity for the desired product.

Keywords

• cobalt
• reductive imination
• Hammett correlation
• recyclability